With the development and wide application of LED illumination, LED phase cut dimming is more and more widely used since it is convenient for user's installation and wire arrangement and it is easy to reconstruct the illuminating circuits that have been laid in the old building into LED illumination solution with dimming function. However, at present, most of the power supply matching LED phase cut dimming produces the dimming effect by altering the output power through the limitation on the input power of the power supply. Such a method has a certain restriction on the load power. When the load power is lower than 70% of the rated output power of the power supply, the dimming effect will become poorer, and there would be poor compatibility with the phase cut dimmer, narrow dimming range and other shortcomings. Some determines the width and cycle of a pulse by detecting the AC signal phase, and uses the width and cycle of such a pulse to determine the output lighting intensity. Although this method solves the problem of the restriction of load power, generally, it adopts the bleeder circuit, which is composed of resistance and capacitance, to improve the compatibility with the dimmer. However, in practical application, the compatibility is still poor. Moreover, it has such disadvantages as great power loss and heat radiation. When the dimmer with poor compatibility is used for dimming, the AC signals after chopping are random. In addition, the AC signal phase detected with the method of AC phase detection is in disorder, the frequency and pulse width of the pulse signal generated finally keep changing, which is prone to cause serious flickering of light.
To sum up, the LED phase cut dimming power supply in other existing technologies has restriction on load power, poor compatibility with the phase cut dimmer or silicon controlled dimmer, great heat radiation, narrow dimming range, proneness to light flickering, poor dimming effect and other defects.